J. P. Ewert

Single unit response of the Toad's (Bufo americanus) caudal thalamus to visual objects

SummaryIn the toad, Bufo americanus, single units of the caudal thalamus were sensitive to either moving or stationary visual objects. Furthermore, some units responded to tactile as well as visual stimulation. On the basis of analysis of the response characteristics of more than 300 single units, the following provisional classification is proposed:1.Spontaneously active units which did not seem to have sensory inputs.2.Units which responded only to tactile stimulation (usually bilateral). The ipsilateral input was typically weaker than the input from the contralateral skin.3.Units with relatively small excitatory receptive visual fields (ERF: 15°–30°) that were best activated by moving black objects of 10° or more in size. To diffuse light changes they showed “off”-responses.4.Large-field units whose excitatory receptive fields (ERF) included the entire contralateral visual field, or the whole visual field, as seen via both eyes. Most of these units were typically responsive to each new kind of object motion, but they quickly adaptated to a repeated movement within a particular region of the field.5.Units that seemed to be variants of types 3 and 4 had ERFs that could change their size, according to circumstances that are not yet known: (a) “Small field” units that could double their size along either the horizontal or vertical axis, (b) Large field units that had a distinct “blind area” centered about the rostral midline; the width of this blind spot could narrow down from the usual 60° distance to only 20–10°. (c) Large field units that were continuously sensitive to the ipsilateral eye, but following tactile stimulation of the contralateral side would respond to contralateral visual movement as well.6.Units that were maximally stimulated by dark objects moved in the “z-axis”. Although the ERF usually included the entire visual field, movements toward the eye from the dorsal direction were most effective.7.Darkness-sensitive units included (a) those with a tonic discharge following the dimming of room lights, and (b) others that gave tonic discharge to light-on and were inhibited during darkness.8.Spontaneously active units with either excitatory (ERF) or inhibitory receptive fields (IRF) that seemed to include the entire visual field. Any moving object within the IRF caused an immediate inhibition, followed by a gradual return of activity to the background level. Some of these units also had a smaller ERF within a large IRF.9.Units activated by moving objects that continued to discharge for 10 seconds or more after the object had disappeared (“memory-units”).10.Units with some of the above characteristics that had the additional property of giving a prolonged response to stationary objects. The ERF-sizes varied from 30° to 90°.

Prey-selective neurons in the toad's optic tectum and sensorimotor interfacing: HRP studies and recording experiments

Summary1.In accordance with recent recording experiments in paralyzed toadsBufo bufo (L.) neurons have been identified between layers 6 and 8 of the optic tectum that exhibit selective responses to the configuration of moving prey dummies.2.Injection of HRP into the two extrinsic tongue muscles — which are the effectors of the toads snapping response — showed that motoneurons innervating the protractor (m. genioglossus) and the retractor (m. hyoglossus) have distinct topographical distributions within the hypoglossal nucleus of the medulla oblongata.3.Following injection of HRP in the vicinity of the hypoglossal nucleus, retrogradely labelled fibers have been identified in (1) the dorso-lateral tegmentum, (2) the fasciculus tegmentalis, (3) ansulate commissure of the ventral tegmentum, and (4) layer 7 of the optic tectum. Retrogradely labelled cells were identified in (1) the subtectal region, (2) the nucleus antero-ventralis tegmenti mesencephali, and (3) layer 6 of the optic tectum. Labelled cells were also identified in the caudal part of the area ventrolateralis thalami, occasionally in the lateral part of the posterocentral nucleus, and in the postero-lateral nucleus of the caudal thalamus.4.The results are discussed with regard to the control of prey-catching behavior, and it is suggested that the toads optic tectum contains a substrate for sensorimotor interfacing.

Visual structures and integrated functions

Overview.- Neural Mechanisms of Visuomotor Coordination: The Evolution of Rana computatrix.- A Prospectus for the Fruitful Interaction Between Neuroethology and Neural Engineering.- From the Retina to the Brain.- A Computer Model to Visualize Change Sensitive Responses in the Salamander Retina.- Properties of Retinal and Retino-Tecto-Isthmo-Tectal Units in Frogs.- Distributed Processing in Vestibulo-Ocular and Other Oculomotor Subsystems in Monkeys and Cats.- Optic Chiasm Hemisection and the Parsing of Visual Information in Frogs.- Approach and Avoidance.- Directed Movement in the Frog: A Closer Look at a Central Representation of Spatial Location.- Prey-Catching and Predator Avoidance 1: Maps and Schemas.- Prey-Catching and Predator Avoidance 2: Modeling the Medullary Hemifield Deficit.- A Neural Network Model for Response to Looming Objects by Frog and Toad.- Control of Frog Evasive Direction: Triggering and Biasing Systems.- Approach and Avoidance Systems in the Rat.- Computation of Absolute Distance in the Mongolian Gerbil (Meriones unguiculatus): Depth Algorithms and Neural Substrates.- Generating Motor Trajectories.- Equilibrium Point Mechanisms in the Spinal Frog.- Actuator and Kinematic Redundancy in Biological Motor Control.- Motor Pattern Generators in Anuran Prey Capture.- From Tectum to Forebrain.- The Striatum and Short-Term Spatial Memory: From Frog to Man.- Multiple Brain Regions Cooperate in Sequential Saccade Generation.- Striato-Pretecto-Tectal Connections: A Substrate for Arousing the Toads Response to Prey.- Cortical Circuitry Underlying Visual Motion Analysis in Turtles.- Computational Significance of Lamination of the Telencephalon.- Information Processing in the Temporal Lobe Visual Cortical Areas of Macaques.- Development, Modulation, Learning, and Habituation.- Neural Mechanisms of Song Learning in a Passerine Bird.- Hormonal Regulation of Motor Systems: How Androgens Control Amplexus (Clasping) in Male Frogs.- Sensorimotor Learning and the Cerebellum.- Modulation of Prey-Catching Behavior in Toads: Data and Modeling.- Learning-Related Modulation of Toads Responses to Prey by Neural Loops Involving the Forebrain.- Dishabituation Hierarchies for Visual Pattern Discrimination in Toads: A Dialog Between Modeling and Experimentation.

Concepts in vertebrate neuroethology

Abstract Neuroethology is concerned with the analysis of the neural substrates and mechanisms that underlie behaviour. In 1951, Tinbergen implied the following goals of Ethophysiology, today known as Neuroethology: (1) recognition and localization of behaviourally meaningful stimuli, e.g. key stimuli; (2) sensorimotor interfacing and feedback interactions; (3) modulations according to internal states and acquired information; (4) motor pattern generation; and (5) ontogenetic and phylogenetic aspects. Using the toads ( Bufo bufo ) visually-guided prey-catching behaviour as an example, experimental strategies and concepts of vertebrate Neuroethology can be demonstrated: (i) visual space is mapped in the brain in a multiple manner; (ii) specification of neurons results from inhibitory and/or excitatory interactions among and within space-mapped neuronal networks; (iii) specialized neurons, e.g. those with stimulus recognition and localization properties, show information processing that takes place in functional units of cell assemblies (so-called ‘neuronal machines’ or ‘brain chips’); (iv) activation of motor pattern generators for different behavioural actions may require coincidence of inputs from different combinations of specialized neurons that serve as command elements and together form a command system; (v) a command system can be regarded as a sensorimotor interface fulfilling tasks with respect to (a) visual pattern recognition and localization, (b) command functions, by initiating the activation of the motor pattern generation system, (c) motor pattern generation through participation in the temporal sequence of the positive feedback from the motor system, and (d) integration of modulatory inputs according to internal states; (vi) the motor pattern generation circuitry consists of a neuronal network capable of producing a consistent distribution of excitation and inhibition and whose output has privileged access to the required motoneuronal pools; (vii) the basic principles of prey selection and motor pattern generation of prey capture emerge in the post-metamorphic juvenile toad with the transition to land and without previous prey experience. During early ontogeny the acuity of sensory discrimination and the performance of motor patterns are subject to maturation paralleled by neural differentiations in the bbrain. performance of motor patterns are subject to maturation paralleled by neural differentiations in the brain. those are programmed and, in amphibians, presumably less dependent on the interaction with the environment than in mammals. This of course does not exclude the possibility of modulating, modifying, specifying and/or extending the visual pattern recognition system of toads due to internal states and individual experience.

Der Einfluß von Zwischenhirndefekten auf die Visuomotorik im Beute- und Fluchtverhalten der Erdkröte (Bufo bufo L.)

SummaryThe prey-catching behaviour of Anura is released by small visual patterns. When toads (Bufo bufo L.) are about to catch food, their first action is turning movement (Rz) towards prey (Sz), visual stimulus pattern): Sz → Rz. It was found that the following stimulus parameters determine the reactivity Rz: angular velocity, stimulus size, and direction of the contrast. Angular Velocity. For angular velocities of 30 to 60°/sec is Rzat a maximum. Rz=0 if the velocity=0 or >200°/sec (Fig. 3). Angular Size. Horizontally moved horizontal rectangular patterns have a greater releasing value than vertical rectangular patterns (Figs. 5A–7A). The releasing effect of a rectangular pattern depends on its horizontal h and vertical v expansion. On principle, an elongation of the vertical edge has inhibiting effects on Rz(Fig. 6A), an elongation of the horizontal edge, however, has stimulating effects (Fig. 5A). Rzpartly is determined by the proportion of the edge lengths h/v; Rzis decreasing if h/v}<1 and it is increasing if h/v>}1 (Fig. 8). For h/v=1 Rzis at a maximum, if h·v = 4°·4° to 8°·8° (Fig. 4A). If h·v}>32°·32° the toads often react by movements aiming at turning away (Ra) from the stimulation locality (Sa): Sa → Ra (escape behaviour). The reactivity of turning away Radepends as well on the angular velocity and the angular size of the visual pattern (Figs. 3 and 10). Direction of Contrast (white pattern on black background or vice versa). In case of black patterns (Figs. 4A, b to 7A, b) the reactivity Rzdepends to a far greater extent on the ratio h/v than in case of white patterns (Figs. 4A, a to 7A, a). Consequently white patterns have in general a greater releasing value than black ones. The reactivity of turning away Ra, however, is much stronger in case of black patterns than in case of white ones.In stimulation the prey-catching behaviour by motivational factors (additional olfactory stimulation) the characteristic depending on h/v is reduced (Fig. 9a and b).Prey-catching movements (turning towards prey, snapping) can be also released by electrical point stimulation of the projection area of the retina in the tectum opticum. Escape movements (turning to flight, crouching, jumping), however, are mainly activated by electrical stimulation of the pretectal region or the caudal dorsal thalamus (Fig. 13).After disturbing the pretectal region and the dorsal thalamus, TP-Iesion (Figs. 2, 11 and 12), escape behaviour fails, whereas the visually released movements in prey-catching behaviour are “disinhibited” (Fig. 10). The animals then respond also to great moving patterns by prey-catching reactions (Sa→ Rz), which before the operation would normally have caused escape (Sa → Ra). Independent of the ratio h/v Rzis increasing with growing area h·v and approaching to a “saturation value” (Figs. 4B–7B).The data obtained in behavioural experiments are compared with findings of corresponding neurophysiological experiments with the frogs retina (Grüsser et al.). The presumable “stimulus/reaction mechanism” is discussed (Fig. 15).ZusammenfassungEine Erdkröte (Bufo bufo L.), die sich in Beutestimmung befindet, antwortet auf ein kleines, in der Horizontalen um sie herum bewegtes visuelles Muster Szmit orientierenden Wendereaktionen Rz, Sz → Rz. Die Reaktivität im Zuwenden Rzist von verschiedenen Parametern des visuellen Reizes Szabhängig: u. a. von der Winkelgeschwindigkeit, der Gestalt, der Flächengröße und dem Vorzeichen des Reiz-Hintergrund-Kontrastes. Die Winkelgeschwindigkeit. Für Sehwinkelgeschwindigkeiten von 30–60°/sec ist Rzmaximal; Rz=0, wenn die Geschwindigkeit=0 oder >200°/sec. Die Gestalt. Die Auslösewirkung einer Rechteckfläche ist von ihrer Horizontal-(h) und Vertikalausdehnung (v) abhängig. Verlängerung der Vertikalkante wirkt auf Rzgrundsätzlich hemmend, Verlängerung der Horizontalkante dagegen stimulierend. So wird Rzz.T. durch das Kantenlängenverhältnis h/v bestimmt: Rzsinkt, wenn h/v<1 und steigt, wenn h/v>1. Die Flächengröβe. Für h/v=1 ist die Reaktivität Rzauf Flächen von h·v=4°·4° bis 8°·8° maximal. Wenn h·v>32°·32°, antworten die Kröten oft mit Bewegungen, die ein Abwenden Ravom Reiz Sazum „Ziele“ haben, Sa→ Ra (Funktionskreis: Flucht). Die Reaktivität im Abwenden Raist ebenfalls von der Bewegungsgeschwindigkeit und der Flächengröße des visuellen Musters abhängig. Das Vorzeichen des Reiz-Hintergrund-Kontrastes (weiße Fläche auf schwarzem Hintergrund oder umgekehrt). Bei schwarzen Flächen ist die Abhängigkeit der Reaktivität Rzvom Kantenlängenverhältnis h/v deutlicher ausgeprägt als bei weißen. Dementsprechend lösen weiße Flächen allgemein stärker aus als schwarze. Die Reaktivität im Abwenden Raist dagegen auf schwarze Flächen sehr viel höher als auf weiße.Durch Erhöhung der Beutestimmung bei zusätzlicher olfaktorischer Reizung (Mehlwurmkotduft) wird die h/v- und h·v-abhängige Spezifität von Rzreduziert.Beutefangbewegungen (Zuwenden, Schnappen) lassen sich auch durch punktförmige elektrische Reizung des retinalen Projektionsfeldes im Tectum opticum auslösen. Fluchtbewegungen (Abwenden, Ducken, Springen) werden dagegen überwiegend durch elektrische Reizung der praetectalen Region oder des caudalen dorsalen Thalamus aktiviert.Nach Ausschaltung der praetectalen Region und des dorsalen Thalamus fällt das visuelle Fluchtverhalten aus; die Visuomotorik im Beutefang ist dagegen „enthemmt“. Die Tiere beantworten dann auch große visuelle Bewegungsmuster mit Beutefangreaktionen (Sa → Rz), die vor der Operation Flucht ausgelöst hatten (Sa → Ra). Unabhängig vom Verhältnis h/v steigt Rzmit zunehmender Flächengröße h·v an und nähert sich dabei einem Sättigungswert.Die Versuchsergebnisse geben weitere Einblicke in die Reizverarbeitung der Visuomotorik im Beute- und Fluchtverhalten der Anuren. Die verhaltensphysiologischen Ergebnisse werden mit neurophysiologischen Befunden an der Froschnetzhaut verglichen (Grüsser et al.). Der mutmaßliche „Reiz-Reaktionsmechanismus“ wird diskutiert.

Movement-sensitive neurones in the toad's retina

Summary1.Neuronal classes. Recordings from single optic nerve fibers of the common toad Bufo bufo (L.) have revealed three types of retinal ganglion cells which correspond to classes II, III and IV in the frog.2.Receptive field organization. All neurones have a central excitatory field, ERF, surrounded by an inhibitory one, IRF (Fig. 10a, b). The ERF for each cell class was ERFII ≈ 4°, ERFIII ≈ 8°, ERFIV = 12–15°.3.Illuminance change over the entire visual field had no effect on class II neurones, produced an “on — off” response in class III and an “off” response in class IV (Fig. 2b–c).4.Angular size of stimuli moved through the central rezeptive field (constant angular velocity and stimulus background contrast). (i) Squares: As the edge length approached the ERF diameter, the discharge rate of all neurones increased, then decreased for larger squares which activated the inhibitory surround (Figs. 3, 4a). (ii) Extending a vertical stripe in the horizontal direction of movement had a similar effect (Fig. 4b). (iii) Elongating a horizontal stripe by more than 2° in the direction of movement produced no change in the discharge rate (Fig. 4c). (iv) Simultaneous movement of two stimuli a and b through the ERF caused a greater discharge than for either allone. Responses to a in the ERF were inhibited if b was in the IRF (Fig. 5).5.Increased angular velocity (constant contrast and angular size) produced increased activation of all neurones (Fig. 6a–d). The degree of increase was different in each neuronal class (Fig. 7A).6.Stimulus background contrast (constant angular size and velocity). The discharge rate generally increased for increasing contrast between stimulus and background (Fig. 8). A white stimulus against black background produced maximal activation of class II neurones; black on white was maximally effective for the other two classes (Fig. 9a–c).7.Input-output functions. A power function best describes the relationships between impulse frequency and (i) stimulus angular velocity, and (ii) stimulus background contrast (Eqs. 9, 11). Impulse frequency is logarithmically dependent on stimulus area (Eqs. 3–6).8.Retinal output and visual behaviour. The neurophysiological findings are compared with quantitative results previously obtained from corresponding behavioural experiments concerning visually induced prey-catching and avoidance reactions.

Größenkonstanzphänomene im Beutefangverhalten der Erdkröte (Bufo bufo L.)

SummaryThe aim of this report is to answer the following questions: a) To what extent does the prey-catching activity of a toad change as the distance between it and a prey-dummy changes while at the same time the size of the visual angle or the absolute size of the dummy are held constant? b) Does the toad prefer a particular angular size in order to catch prey or can it recognize—irrespective of the distance— a particular absolute object size which is optimal for its behaviour?1)For constant absolute or visual angular size of a prey-dummy, the prey-catching turning activity generally falls off with increasing distance between animal and dummy (Fig. 2).2)If square dummies are presented to toads from a constant distance, then a particular dummy size elicits maximal prey-catching activity. When the distance is varied, this optimal size remains constant when measured in absolute units of length (“size-constancy” phenomenon); the edge length of such an optimal dummy is of about 7 mm (Table 1). On the visual angle scale (which is not absolute), the optimal value accordingly shifts towards smaller values for distant objects, towards larger values for objects nearer to the animal (Fig. 4).3)For the orientingturning reaction of the prey-catching sequence object size-constancy is independent of binocular vision (Table 1; compare Fig. 4A and B). However, insnapping behaviour, this phenomenon is linked to the information leaving both eyes (Table 1; compare Fig. 5A and B).4)It was not possible to demonstrate the size-constancy phenomenon after the thalamus-pretectal region has been destroyed. Presumably it is in the nuclei of this region that one should look for neurons which—like certain cells in the human visual cortex—“fit” their excitatory receptive field size to the specific object distance in question.ZusammenfassungIn der vorliegenden Arbeit sollten folgende Fragen beantwortet werden: a) Inwieweit ändert sich die Beutefangaktivität der Erdkröte, wenn man die Distanz zwischen Tier und Beuteobjekt variiert und hierbei die Sehwinkelgröße oder die absolute Objektgröße konstant hält? b) Bevorzugt die Kröte unter Beuteobjekten stets eine bestimmte Sehwinkelgröße oder erkennt sie — unabhängig von der Distanz — eine bestimmte absolute Objektgröße als optimal für ihr Fangverhalten.1.Bei konstanter Absolut- oder Sehwinkelgröße einer Attrappe sank die Beutefangwendeaktivität generell mit zunehmender Attrappen-Distanz ab.2.Unter quadratischen Objekten, die der Kröte in konstantem Abstand geboten wurden, löste eine bestimmte Größe maximale Beutefangaktivität aus. Bei Variation des Abstandes blieb diese optimale Größe über der metrischen Skala konstant („Größenkonstanz-Phänomen”); siebetrug ca. 7 mm Kantenlänge. Dementsprechend verschob sich der Optimalwert auf der Sehwinkelgradskala für entfernte Objekte in Richtung kleiner Werte, für nahe in Richtung großer.3.Objektgrößenkonstanz war für die orientierendeWendereaktion des Beutefangs auch bei einäugigen Kröten nachweisbar.Im Schnappverhalten war dieses Phänomen jedoch an das binokulare Sehen gebunden.4.Nach Ausschaltung der Thalamus-Praetecum-Region waren Größenkonstanz-Phänomene nicht mehr eindeutig nachzuweisen. Vielleicht sind in diesem Kerngebiet Neurone zu suchen, die — ähnlich wie im visuellen Cortex des Menschen — ihre excitatorischen rezeptiven Feldgrößen der jeweiligen Objektdistanz über „z-Achsen-Lokalisationsmechanismen” anpassen.

Reaktionscharakteristik von Neuronen aus dem Tectum opticum und Subtectum der Erdkröte Bufo bufo (L.)

SummaryIn the European toad Bufo bufo (L.) activity from single neurons in the midbrain (tectum opticum, sub-tectum and tori semicirculari) could be elicited by visual, tactile, acoustic or vibratory stimulation (Fig. 3). Furthermore bi- and trimodal units were found. By means of single cell recording experiments in demobilized animals the present paper gives preliminary data about localization and response characteristics. These categories are related to some behavioural observations on toads normally and during brain stimulation (Fig. 6).1.Visual units with smaller excitatory receptive fields (optic tectum: they seem to be located mostly in the stratum griseum centrale). Among units with ERFs of 10–20° many were found with the expected retinotopic location in the tectum (Fig. 2); however others were „dislocated“ up to 20° by comparison with the more dorsal retinal fiber terminals. These units responded only to moving stimuli with good contrast (Figs. 4 and 5 A) and habituated after a movement through the ERF. The function of these units seems linked to the prey-catching behaviour that can be evoked from these regions through chronically-implanted electrodes (Fig. 6B).2.Visual units with large ERFs (optic tectum: they seem to be located mostly in the stratum periventriculare). They showed activity specific to object movements of three types: a) within the rostral visual field of the contralateral eye, b) within the lower visual field of the contralateral eye, c) within the total field (Fig. 7, I-III).3.Units were found within sub-tectal regions that were activated by touching the contralateral body skin, especially around the head. Focal electrical brain stimulation of this region produces eye or mouth-wiping behaviour in the freemoving toad (Fig. 6A).4.Some units of the sub-tectal region could be activated by vibratory stimulation (“substrate-borne-sound”, Fig. 8A and B) but not by acoustic stimulation (“airborne sound”).5.Among units of the sub-tectum and the tori semicirculari sensitiv to acoustic stimulation three types were distinguished: a) “wide band” units with maximum sensitivity between 800 and 1000 Hz, and with a silent zone at about 500 Hz, b) “narrow-band” units with maximal sensitivity in this 500 Hz region and c) “narrow-band” units with best response between 1000–1200 Hz (Fig. 9a–c).6.Two types of sub-tectal units sensitive to contralateral tactile and visual inputs were found; they were particularly excited by large moving objects: a) The whole field included the visual ERF (Fig. 10, IIIo,t). b) The visual ERF included the lower field of the contralateral eye; these units had also vibratory inputs (Fig. 10, IIo,v,t).7.Units of the sub-tectal region with combined visual and vibration sensitivity, on the other hand, had visual ERFs that were confined to the frontal field of the contralateral eye (Fig. 10, Io,v).8.Visual-acoustic units of sub-tectal regions respond to either a dimming of the ERF (“off”-response) or to sounds with maximum sensitivity at 1000 Hz.9.Some sub-tectal units were activated by vibration, but the activity could be suppressed by simultaneous sounds of about 500 Hz.ZusammenfassungAus dem Mittelhirn (Tectum opticum, Sub-Tectum, Tori semicirculari) der Erdkröte Bufo bufo (L.) wurden Neuronen registriert, die optische, taktile, akustische oder vibratorische Eingänge haben. Darüber hinaus wurden bi- und trimodale Einheiten gefunden. In der vorliegenden Arbeit wird anhand von Einzelzellableitungen am demobilisierten Tier ein erster Überblick über deren Lokalisation und Reaktionscharakteristik gegeben. Hirnreizungs-Experimente am freibeweglichen Tier sowie korrespondierende verhaltensphysiologische Versuche erlauben Hinweise auf ihre verhaltensbiologische Relevanz.1.Optisch erregbare Neuronen mit relativ kleinen exzitatorischen rezeptiven Feldern, 10°≦ERF≦20° (Tectum opticum : hauptsächlich Stratum griseum centrale). Von einigen wurde die retino-tectale Projektion im Tectum „wiederholt“; bei anderen konnten gegenüber den ERF zugeordneter Netzhautneuronen „Dislokationen“ bis zu 20° auftreten. Sie wurden nur durch kontrastgebende bewegte Objekte aktiviert und adaptierten nach einmaliger Felddurchquerung relativ stark. Elektrische Reizung dieser Hirnbezirke löste beim freibeweglichen Tier entsprechend orientierte Beutefang-Wendereaktionen aus.2.Optisch erregbare Neuronen mit relativ großen ERF (Tectum opticum: hauptsächlich Stratum periventriculare). Sie waren ebenfalls bewegungsspezifisch. Drei Typen wurden gefunden: a) ERF: vorderes Gesichtsfeld des kontralateralen Auges; b) EBF: unteres Gesichtsfeld des kontralateralen Auges; c) ERF: ganzes Gesichtsfeld.3.Taktil erregbare Neuronen (subtectale Regionen). Sie wurden aktiviert, wenn man die zum Ableitort (Hirnhälfte) kontralaterale Körperseite, hauptsächlich die Kopfbezirke taktil reizte. Elektrische Hirnreizung dieser Region löste beim freibeweglichen Tier Wischbewegungen aus.4.Vibrations-sensitive Neuronen (subtectale Region). Sie antworteten nur auf Vibrationsreize (Körper-Schall) nicht dagegen auf akustische Reize (Luft-Schall).5.Akustisch erregbare Neuronen (subtectale Regionen, Tori semicirculari). Diese Einheiten ließen sich nur durch Luft-Schall aktivieren. Drei verschiedene Typen wurden gefunden; a) „Breitband-Neuronen“ mit maximaler Empfindlichkeit zwischen 800 und 1000 Hz; bei 500 Hz trat eine „Hör-Lücke“ auf; b) „TieftonNeuronen “(Bereich um 500 Hz); c) „Hochton-Neuronen“ (Bereich um 1000 bis 1200 Hz).6.Optisch-taktil erregbare Neuronen (subtectale Regionen). Sie wurden durch relativ große bewegte Objekte aktiviert. Das mechanorezeptive Feld des taktilen Eingangs erstreckte sich auf die kontralaterale Körperseite. Zwei Typen wurden gefunden: a) Das visuelle ERF schloß das ganze Gesichtsfeld ein; b) das visuelle ERE umfaßte das untere Gesichtsfeld des kontralateralen Auges; dieser Neuronentyp ließ sich auch durch Vibrationsreize aktivieren.7.Optisch-vibratorisch erregbare Neuronen (subtectale Regionen). Das visuelle ERF erstreckte sich auf das frontale Gesichtsfeld des kontralateralen Auges. Dasselbe Neuron antwortete auch auf Vibrationsreize.8.Optisch-akustisch erregbare Neuronen (subtectale Bereiche). Sie antworteten sowohl auf Beschattung des Auges („off“-Reaktion) als auch auf Tonreizung (1000 Hz).9.Vibratorisch-akustisch erregbare Neuronen (subtectale Regionen). Sie wurden durch Erschütterungsreize aktiviert. Bei gleichzeitiger Tonreizung (500 Hz) war die Antwort gehemmt.

Visual pattern discrimination through interactions of neural networks: a combined electrical brain stimulation, brain lesion, and extracellular recording study inSalamandra salamandra

SummaryIn freely movingSalamandra salamandra various brain sites (n = 33) were stimulated monopolarly via chronically implanted electrodes. Stimulation of the optic tectum mainly elicited prey-catching behavior (mean lower current threshold Ilt = 9 μA) and sometimes predator-avoidance behavior (Ilt = 28 μA). Stimulation of the caudal dorsal (Ilt = 27 μA) or rostral dorsal thalamus (Ilt = 26 μA) exclusively released avoidance movements, such as ipsiversive turning, running, or moving backward. Telencephalic stimulation (Ilt = 66 μA) activated backward-creeping, trunk-raising, or jaw-opening/closing.Brain lesions were produced inn = 64 fire salamanders either by anodal DC current, radiofrequency current, Kainic acid micro-injections, or micro-knife cuts. After ablation of the optic tectum, both visually guided prey-catching and predator-avoidance behaviors failed to occur. Unilateral lesions in the following prosencephalic brain areas caused a strong deficit of configurational prey-selection (‘disinhibition of prey-catching behavior’) and a failure of visual predator-avoidance behavior in response to stimuli moving in certain areas of the visual field: (i) caudal dorsal thalamus (entire contralateral visual field), (ii) rostral dorsal thalamus (frontal visual field of both eyes), and (iii) medial pallium (entire visual field of both eyes). Lesions in the lateral pallium led to a decrease in the threshold of visually guided predator-avoidance behavior.Action potentials were extracellularly recorded from single tectal T5 neurons in intact animals and following various prosencephalic lesions (i), (ii), or (iii). In all of then = 14 investigated neurons the same alteration of response properties was obtained, corresponding to the change in behavior. Recordings from a single prey-selective class T5(1) neuron pre and post DC coagulation in the ipsilateral caudal dorsal thalamus produced: an increase in the diameter of the excitatory receptive field (ERF) from ≈30 ° to ≈50 ° and a strong deficit in selectivity with regard to moving configurational visual stimuli.

Musterauswertung durch Tectum- und Thalamus/Praetectum-Neurone im visuellen System der KröteBufo bufo (L.)

SummaryQuantitative behavioral experiments demonstrated that toads discriminate moving prey and enemy objects mainly by two surface parameters: (i)Object expansion in the direction of movement generally means “prey” (Fig. 7Ca) while (ii)expansion perpendicular to the direction of movement signifies “not prey” or “enemy” (Fig. 7Cb). Single unit recordings along the central visual path should answer the question as to whether there are neuronal nerve nets responsible for processing those behaviorally relevant surface parameters of moving visual objects (Figs. 1 and 2).1.In the thalamus/pretectal region (mainly the caudal dorsal thalamus; see Fig. 3) units with circular excitatory receptive fields (ERF) of about 46 ° diameter were investigated. During successive experiments the discharge rate of these neurons was increasing only when the expansion of an object — moved through the center of the receptive field—was increased perpendicularly to the direction of motion, (Figs. 5Ab, c and 6A). (The stimulus parameters of contrast and angular velocity were held constant.)2.In the optic tectum (stratum griseum et album centrale; see Fig. 4), units were identified showing circular ERFs of about 27 ° diameter. Some of these neurons (tectum 1 neurons) were activated mainly by increasing object expansion in the direction of movement (Figs. 5Ba, c and 6B).3.Other units of the same tectal layer (tectum 2 neurons) differed from tectum 1 neurons as follows: The discharge rate diminished according to the increasing surface expansion of the stimulus object perpendicular to the direction of movement. The response of those neurons “reflected” the key stimulus “prey” (Figs. 5C and 6C; compare Figs. 7 B and C).4.It is supposed that prey/enemy recognition is a result of subtractive and additive interactions between tectal and thalamus/pretectal “gestalt” filters (Fig. 8). The response characteristic of tectum 2 neurons to the size of a moving stimulus may be the result of excitatory inputs from tectum 1 and inhibitory from thalamus/ pretectal neurons (Fig. 8; compare Figs. 7 A and B). Presumably those units (Fig. 7 B) act as a “trigger system” for the prey-orienting movement (Fig. 7C).ZusammenfassungFrühere quantitative Verhaltensexperimente hatten ergeben, daß die Kröte für die Unterscheidung „Beute/Feind” hauptsächlich zwei Flächen-parameter eines bewegten Objektes nutzt: (a) die Objektausdehnungin der Bewegungsrichtung — sie bedeutet generell Beute; (b) die Ausdehnungquer zur Bewegungsrichtung — sie bedeutet generell „keine Beute” oder „Feind”. Mit Hilfe von Einzelzellableitungen wurde geprüft, ob es im zentralen visuellen System der Kröte Neurone gibt, die an der Auswertung solcher Gestaltparameter beteiligt sind.1.In der Thalamus/Praetectum-Region (überwiegend caudaler dorsaler Thalamus) wurden Neurone mit zirkulären excitatorischen rezeptiven Feldern (ERF) von ca. 46 ° ø quantitativ untersucht. Wenn man unterschiedliche rechtwinklige Objekte durch das rezeptive Feldzentrum bewegte, so stieg die neuronale Entladungsrate in successiven Versuchen lediglich mit zunehmender Ausdehnung eines Objektsquer zur Bewegungsrichtung an. (Die Werte für die Parameter Kontrast und Winkelgeschwindigkeit wurden konstant gehalten.)2.Im Tectum opticum (Stratum griseum et album centrale) konnten Neurone identifiziert werden, die ein zirkuläres, ca 27 ° gro\es ERF hatten. Einige von ihnen (Tectum-1-Neurone) gaben hauptsächlich Objektausdehnungenin der Bewegungsrichtung durch Modulation ihrer Entladungsrate an; hierbei erhöhte sich die Entladungsrate — in Grenzen — mit zunehmender Ausdehnungskomponente der Reizfläche.3.Andere Einheiten aus denselben Tectum-Schichten (Tectum-2-Neurone) unterschieden sich von den ersten hauptsächlich dadurch, daß die Entladungsrate auf Flächen-Ausdehnungskomponentenquer zur Bewegungsrichtung gesenkt wurde. Ihre Antwortcharakteristik „spiegelte” sehr gut den Schlüsselreiz „Beute” wider.4.Es wird vermutet, daß der Beute/Feind-Erkennungsprozeß auf subtraktiver und additiver Interaktion zwischen den tectalen und thalamus-praetectalen „Gestalt”-Filtern beruht. Hierbei könnte sich die Antwortcharakteristik von Tectum-2-Neuronen für unterschiedliche Flächenmuster durch erregende Eingänge von Tectum-1- und hemmende Eingänge von Thalamus/Praetectum-Neuronen ergeben.